The present invention relates to a method for producing ethylene sulfite or refined ethylene sulfite which is useful for an application to an electrolyte.
Ethylene sulfite is used as a raw material in various fields of organic synthesis, and a solvent or an additive for an electrolyte of a lithium secondary battery or the like.
Examples of conventional methods for producing the ethylene sulfite are:    i) a method of reacting ethylene glycol and thionyl chloride;    ii) a method of reacting ethylene glycol and dimethyl sulfite;    iii) a method of reacting ethylene oxide and sulfur dioxide;    iv) a method of depolymerizing polyethylene sulfiteAmong these methods, the method of reacting ethylene glycol and thionyl chloride has been considered advantageous industrially due to safety and low costs.
D. S. Bleslow and H. Skolnic, Chem. Heterocycl. Compound., 1966, 21-1,1 describes the method of reacting ethylene glycol and thionyl chloride for producing ethylene sulfite without solvent and catalyst.
However, ethylene sulfite produced by the above conventional methods contains a large amount of impurities.
The ethylene sulfite produced by the conventional methods is unsuitable for a solvent and an additive for an electrolyte for a lithium secondary battery, since the ethylene sulfite contains impurities so much that the electrolyte does not have good storage stability. For example, the electrolyte containing the ethylene sulfite produced by the conventional methods tends to cause an increase of acid content during preservation. When the electrolyte is used for a lithium secondary battery, the battery is increased in its internal pressure due to the electrolyte which sometimes damages a canister of the battery.
Thus, there has been required ethylene sulfite having high purity in order to improve performance of the battery.